In the Carl F. Waite et al U.S. Pat. No. 3,213,496 there is disclosed a method whereby the bottom surface of one pattern plate is accurately made to dovetail or match with the top surface of another pattern plate using machined surfaces, which are not precisely located. In the procedure taught by the Waite et al patent, the top and bottom pattern plates are abutted and a hardenable material is injected into each valley and is bonded to the abutting surface of the other pattern plate to produce lugs thereon. In the Waite et al design a great number of valleys are required to be machined and the pattern plates can only be economically produced by performing the machining operations quickly without starting and stopping the machining operations in precise locations. While it might be possible for an operator of a milling machine to produce a second pattern plate having the exact length, arrangement, and spacing of valleys which were produced in a first pattern plate of the Waite et al design, it would be an extremely time consuming, tedious and a very expensive operation. All of the pattern plates which are produced by the Waite et al procedure therefore have a more or less random arrangement of valleys and lugs therein, and each pattern plate will only match the pattern plate from which its lugs were cast. When one of the matching pattern plates of the Waite et al patent is damaged, the remaining pattern plate is useless.
In the Rusk et al, U.S. Pat. No. 3,472,311 there is disclosed a pattern plate having valleys and lugs in the top surface which are directly opposite matching lugs and valleys in its bottom surface, so that the parts made from the bottom surface will exactly match parts made from the top surface. Parts can be made therefore from both the top surface and the bottom surface of a single pattern plate, but in order to accomplish this, the top and bottom surfaces of the same pattern plate must be very accurately laid out and produced. Pattern plates of such a design can only be made economically if the pattern plates are cast from a master copy. This dictates that pattern plates having usable top and bottom surfaces can only be made economically by a casting process, and that the accuracy of the pattern plates so produced is limited to the accuracy of a casting operation. Casting processes always involve shrinkage, and shrinkage in turn produces a cast part which is different from the master part by several thousands of an inch at best. Two pattern plates produced from the same master therefore will have a clearance therebetween of twice the shrinkage that is involved in the casting operation. It goes without saying, therefore, that a cast plate can never exactly duplicate the configuration of the master plate.
An object of the present invention is the provision of a new and improved inexpensive pattern plate configuration and process for producing the same, whereby a plurality of pattern plates can be produced which are so precisely alike that the parts made from one pattern plate precisely match with those produced from another pattern plate.
Another object of the invention is the provision of a new and improved method of producing pattern plates of the above described type wherein the parts which are produced from one pattern plate will actually have an interference fit with respect to the parts produced from another one of the pattern plates.
A further object of the invention is the provision of a new and improved pattern plate configuration and method of machining the same whereby the valleys that are machined in one pattern plate can be quickly duplicated in another pattern plate without requiring time consuming set up time of a milling machine.
Further objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiments described with reference to the accompanying drawings forming a part of this specification.